Manual or Auto Iris Lens?

The iris is the part of the lens that determines how much light falls
upon the camera CCD sensor.

The Manual Iris 'MI' lens has this fixed at the time of installation.
As the light levels change in the scene, the lens can do nothing to
prevent either too little or too much light entering the camera.
Virtually all cameras employ an Automatic Electronic Shutter 'AES' to
compensate for these variations when fitted with an MI lens. However they
are only able to cope with a relatively small change in light levels.

An MI lens should never be used in an external situation, as the camera
will be unable to cope with large changes in light levels. Use an Auto
Iris ‘AI’ lens in this case, or indeed anywhere where large scene
illumination changes take place.

The advent of new sensor technology such as PIXIM may result in a
change to this situation in the future.